52x0.75mm Filter, Neutral Density (ND) 4x for OKS11-35-1 lens
These filters have 52x0.75 mounting thread. I have only one lens suitable for it - LOMO OKS11-35-1 in OCT-18 mount for turret Konvas.
N-4x – is quite strong neutral density filter that reduces light amount 4 times. It can be used to increase shutter speed if necessary (to blur motion, for example).